Dissimilar metals?

[Justaguy10825]

Hello again! I really appreciate this forum & everyone?s help! I hate to sound dumb but I am still pretty new to this stuff. I have a 24? 1993 Sweetwater. As I have said in previous posts, I just added a bigger/heavier engine to the boat & reinforced the engine pod/transom areas as well as adding 3? plates to the bottom of all engine pod bolts & thick aluminum strips to the tops of the frame rails so the bolts don?t easily pull through. It just seemed appropriate to help distribute the weight on the bolt holes to hopefully keep it from falling/tearing off the boat.

I sometimes have a tendency to over analyze things before & after I do them & came across a ?Potential issue?(????) I have read that butting different metals up against each other could be a potential problem. The extra bracing I used on the top & rear bottom of the engine pod are made out of powder coated steel & the 3? plates are also made of steel. All of which are bolted directly to the aluminum. I do not take the boat on saltwater & have no intentions of doing so. It is not stored on the water & really have no plans to do so but who knows, I may consider a slip through the summer months in the future if I get tired of dragging it to & from the water but not sure.

What kind (if any) problems should I anticipate from the aluminum/steel combo?

 

[luckyjr]

Re: Dissimilar metals?

Is all the steel powder coated?

 

[Justaguy10825]

Re: Dissimilar metals?

Is all the steel powder coated?

Yep....

 

[luckyjr]

Re: Dissimilar metals?

spray cold galv in the holes you drilled, it will help but not a cure the problem,

 

[5150abf]

Re: Dissimilar metals?

Other than rust I don't see a problem with that, your car likely has aluminum rims that sit against the steel rotor with no problems.

Stainless will sometimes, but not always, react with aluminum but every screw and fastener on my boat is stainless and I have never had a problem and you are using regular steel so I think you are fine.

 

[WaterDR]

Re: Dissimilar metals?

Whenever you have dissimilar metals in contact with eachother and submerges in water, you will have corrosion. Steel will also simply rust on it's own. Aluminum corrodes too, but aluminum oxide is a natural corrosion barrier to further corrosion.

The problems with galvanic corrosion in fresh water are a lot less of an issue than in salt water.

To solve the problem, don't use dissimilar metals. Using a rubber fitting or using a heavy coat of grease in the screw holes will help miniize the problem. Spraying any sort of galvanized material in the screw holes might work for a short term, but the galvanizd layer will quickly rust away in most envirionments.

I would say don't powder coat. Why? Because as soon as any part of the power coat material breaks off or wears off, you kow have a small part of the metal surface bearing the full brunt of the electrolysis. As such, rather than have a small amount of corrosion over a larger surface, you will have a large amount of corrosion over a much smaller area and eat right throught he metal. This depends, however, on which metal you coat....the more noble, or the least noble one. The least noble metal will act as the annode which is where you will have metal loss.

 

[luckyjr]

Re: Dissimilar metals?

Cold Galv is what we use for touch up in industrail fabrication and spec out by all major refineries. One example would be my boat. My cross members are galvanazed steel the risers are aluminum after 20yrs at the bolting connection no rust. If the galvanized last, there is not much of a problem but aluminum to aluminum is best.